Surface activity, film formation, and emulsifying properties of milk proteins

Abstract

This overview indicates that simple, reliable standardized methods for measuring emulsifying activity and for determining ES are not yet available. One of the major shortcomings of most of the current methods is the inability to detect very small fat globules (less than 0.5 micron), which may be very important in stable emulsions. Several of the methods are time consuming and destructive. To minimize the time required to evaluate emulsions, techniques that monitor instability under the influence of accelerated aging (increased temperature and gravitational field) have been used with varying degrees of success. These methods, e.g., centrifugation, are useful, but processes occurring during centrifugation or heating may not be characteristic of those occurring in a stored emulsion. Generally, there is no method that simultaneously determines changes in emulsions due to the aggregation coalescence, flocculation, creaming, of the droplets and/or oiling off. No single criterion of emulsion instability is sufficient to characterize all the changes occurring in the system. A nonintrusive technique that can monitor dynamic changes in emulsions is needed. Ideally, it should be simple, rapid, inexpensive, and applicable to both diluted and concentrated emulsions. Scientists must continue research to develop such a standard universal method for determining ES, because data from different laboratories cannot currently be validly compared. Reliable methods are also required to elucidate relationships between the physical properties of proteins as emulsifiers and their performance in food emulsions. There is a need for opportunities for systematic research to determine the interfacial behavior of food emulsifiers, particularly food proteins. Research to describe the kinetics and thermodynamics of adsorption at an interface, the extent of unfolding, the degree of packing and polypeptide interactions in an interface during film formation, and information concerning the physical and mechanical properties of interfacial films is needed to describe emulsifying behavior of different proteins. The effects of components in the continuous and discontinuous phase, parameters of manufacture, and interactions between different types of surface-active materials that occur in food need to be studied.